FIG. 8 shows an outline diagram of a color offset rotary printing machine (rotary press) for performing color printing on paper, film, or the like. In the color offset rotary printing machine, blue printing, red printing, yellow printing, and black printing are performed separately by a blue printing section 81, a red printing section 71, a yellow printing section 61, and a black printing section 51, and color printing is performed while respective colors are being superposed.
That is, during the time that printing paper 93 is moving upward in the direction indicated by an arrow 94, blue printing, red printing, yellow printing, and black printing are performed sequentially by color printing rolls (blanket cylinders) 83, 73, 63, and 53.
Plate cylinder (plate cylinders) rolls 82, 72, 62, and 52 have blue, red, yellow, black printing plates on their cylindrical surfaces, respectively, and the plates are inked with blue, red, yellow, and black. While they are being rotated, the plate cylinder rolls 82, 72, 62, and 52 transfer the respective inks on the printing rolls 83, 73, 63, and 53. The blue, red, yellow, and black inks transferred on the printing rolls 83, 73, 63, and 53 are further transferred on printing paper 93, whereby color printing is performed.
In this case, a roll drive motor 64 rotates the printing roll 63 and plate cylinder roll 62 of the yellow printing section 61 and the printing roll 53 and plate cylinder roll 52 of the black printing section 51 through a driving gear 65. A roll drive motor 84 rotates the printing roll 83 and plate cylinder roll 82 of the red printing section 81 and the printing roll 73 and plate cylinder roll 72 of the red printing section 71 through a driving gear 85. Note that there are cases where each of the color printing sections is provided with a roll drive motor for independently driving the printing roll and plate cylinder roll of each color printing section.
In such a color offset rotary printing machine, high-speed and high-fine printing has been developed in recent years. However, there are cases where printing trouble called “double,” or printing trouble called “out-of-register,” develops. In the printing trouble called “double,” inks to be transferred to the same point on the printing paper 93 are shifted from each other, and in the printing trouble called “out-of-register,” color shift occurs in each color. Therefore, preventing the printing trouble has been strongly demanded.
It is conceivable that the printing trouble results from the rotational phase difference between the color printing rolls 83,73, 63, and 53 that occurs because of torsion vibration in the drive shafts, cutting and mounting errors in the driving gears 65 and 85, etc. It is therefore important to detect a rotational phase difference between the printing rolls with a high degree of accuracy and drive the printing rolls so that the rotational phase difference is eliminated.
A conventional method such as that shown in FIG. 9 has been proposed as a rotational phase difference detecting method for a printing roll system. This rotational phase difference detecting method is called a high-speed pulse clock method and utilizes the internal clock pulse of a color offset rotary printing machine, thereby detecting a rotational phase difference between printing rolls.
In FIG. 9, black-and-white patterns 90 of about 1 mm in pitch, for example, are provided on the outer peripheries of the printing rolls 73, 83. The black-and-white pattern 90 of the printing roll 73 is detected by an optical sensor 91 and the black-and-white pattern 90 of the printing roll 83 is detected by an optical sensor 92. Each of the optical sensors 91, 92 detects the black-and-white pattern 90, for example, by emitting light to the black-and-white pattern 90 and measuring the light quantity of the reflected light.
In this case, an output pulse signal A corresponding to the black-and-white pattern 90 of the printing roll 73 is obtained from the optical sensor 91, and an output pulse signal B corresponding to the black-and-white pattern 90 of the printing roll 83 is obtained from the optical sensor 92.
For example, phase differences Δt1, Δt2, and Δt3 between the output pulse signals A and B are detected by use of an internal clock pulse signal of 10 MHz. Each of the phase differences Δt1, Δt2, and Δt3 corresponds to the rotational phase difference between the printing rolls 73 and 83. Note that the accuracy of detection in this method is determined according to the pitch between the black and white sections of the pattern 90 and the frequency of the internal clock pulse signal.
Since the accuracy of detection in the rotational phase difference detecting method shown in FIG. 9 is determined by the pitch between the black and white sections of the pattern 90 and the frequency of the internal clock pulse signal, it is necessary to reduce the pitch between the black and white sections of the pattern 90 and increase the frequency of the internal clock pulse signal, in order to raise the accuracy of detection. However, if the black-and-white pattern 90 of a small pitch being rotated at high speed is detected with a high degree of accuracy, the optical sensors will need to have high resolution and the rotational phase difference detecting system will become costly.
The rotational phase difference detecting method shown in FIG. 9 also needs to calculate the rotational phase difference between the printing rolls 73 and 83 in consideration of the rotational speed of the rolls, after a phase difference between the output pulse signals A and B is detected. Because of this, a processor with high-speed performance is required for performing the calculation process at high speed and with a high degree of accuracy and makes the rotational phase difference detecting system costly.
As the rotational phase difference detecting method for a roll system, in addition to the aforementioned method, there is a method of measuring the rotational speeds of two rolls with a laser Doppler speedometer and then converting the difference between the rotational speeds to a rotational phase difference. This method, however, requires calculation of integration when converting rotational speed difference to rotational phase difference and cannot obtain accuracy necessary for practical use.
Accordingly, it is an object of the present invention to provide a rotational phase difference detecting system and a rotational phase difference detecting method which are capable of detecting a rotational phase difference between a plurality of rotating bodies with simple construction and a high degree of accuracy.
Another object of the present invention is to provide an operating-state monitoring system and an operating-state monitoring method in which there is no need for a machine operator to monitor a machine at all times, and which are capable of lessening operator's labor, by employing the rotational phase difference detecting system and method.